An organic light emitting device is driven by providing a thin film containing a luminous organic compound between an anode and a cathode, applying a voltage between the electrodes, and injecting a hole and an electron. The hole is recombined with the electron in the device to produce an exciton (excited state) of the luminous organic compound, and the organic light emitting device uses the emitted light when the exciton returns to a ground state.
Recent progress of an organic light emitting device is remarkable, and the characteristics of the device enable a light emitting device with a high luminance at a low applied voltage, a variety of emission wavelengths, high-speed responsiveness, thin shape, and light weight. From this fact, it is suggested that the organic light emitting device have potential to find use in a wide variety of applications.
However, when the application of the organic light emitting device to a display and the like is attempted, the stability of the current device has not been sufficient in practical use. In particular, it has necessary to ameliorate properties thereof due to the problem that light emitting efficiency deteriorates with time when the device is driven continuously.
The cause of the deterioration in the light emitting efficiency may reside in that the organic compound constituting the device deteriorates due to repeated oxidation and reduction by a charge injected from each electrode. It is indicated in Science, 283, 1900 (1999) that a factor of the deterioration of tris(8-quinolilato)aluminum (Alq3) is unstability of a radical cation (cation) generated by hole transport. In addition, Japanese Patent Application Laid-Open No. 2007-70352 discloses that a specific aryl amine compound having resistance to an oxidation reaction is used for the purpose of ameliorating the deterioration.
In addition, another cause thereof may be the deterioration in a material undergoing the excited state of the compound in the emission layer. It is indicated, in Journal of Applied Physics 101, 024512 (2007), that a reaction mediated by the excited state is a factor of the material deterioration.
However, even if the resistance to oxidation and reduction of the compound and the stability at the excited state are ameliorated, the continuous driving durability has not been sufficient in practical use by conventional technologies.